JP2005283402A - Inertia sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inertia sensor provided with a beam compatible in both high sensitivity and impact resistance. <P>SOLUTION: Easily deformable parts (thin thickness of recesses 15, holes or the like) are provided locally while avoiding a portion concentrated with a stress generated in the beam by impact. The recesses 15 are arranged line-symmetrically with respect to a straight line along an extension direction passing the center of the beam 13, and a straight line right-angled to the extension direction. A root part of the beam 13 is formed to form a gentle angle making the root part not contact with a weight 12 and a frame 14 at right angle. The sensitivity of the sensor is enhanced thereby without lowering the impact resistance of the sensor, and a stress concentrating area in the beam root part is dispersed to enhance the impact resistance without sacrificing the sensitivity of the sensor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inertial sensor such as an acceleration sensor or a gyro, and more particularly to an inertial sensor excellent in high sensitivity and impact resistance.

  In recent years, inertia sensors such as accelerometers and gyros have been able to achieve miniaturization, high performance, and low price at the same time due to the development of micromachining technology using MEMS (Micro Electro Mechanical System) technology. . Against this background, inertial sensors as MEMS devices are used for car navigation, in-vehicle airbag control, camera / video camera shake prevention, mobile phone, robot posture control, game gesture input recognition, HDD rotation / impact. As a device for detection or the like, it is expected to be mounted on any device that requires motion detection, and inertial sensors mounted on these devices are required to have higher sensitivity.

  FIG. 1 is a diagram for explaining a main configuration example of a general inertial sensor having a basic configuration in which a weight, which is a movable portion, is suspended by a beam. FIG. 1 (a) is a perspective view of a sensing unit, and FIG. b) is a top plan view of the sensing unit. In these figures, 10 is a substrate for producing a sensing part of the inertial sensor, 11 is a piezoresistor built in the board 10, 12 is a weight that is a movable part of the sensing part, and 13 supports the movement of the weight 12. A plurality of beams are provided. Reference numeral 14 denotes a frame for holding the weight 12 and the beam 13. The beam 13 has a width W, a thickness T, and a length L. When the weight 12, which is a movable part, moves, the movement causes twisting and bending of the beam 13, and the resistance value of the piezoresistor 11 provided on the beam 13 changes. This change in resistance value is the output of the Wheatstone bridge circuit. Obtained as an electrical signal.

By the way, since an unexpected large impact can sometimes be applied to a device that detects motion, there is a risk that a large impact is applied to an inertial sensor mounted on the device. Since a general inertial sensor has a basic configuration that suspends a weight, which is a movable part, with a beam, if a large impact is accidentally applied, the beam will be greatly deformed or damaged, and will not function as a sensor. Such a problem is known (Patent Document 1). For example, in an automobile application such as an in-vehicle airbag, a large impact that cannot occur during normal operation can be applied in the case of a rear-end collision or rollover, and in a mobile device or the like, an impact when the device is accidentally dropped is expected. In addition, in hobby applications such as game machines, an extremely large impact can occur when the user performs rough handling. Such an accidental impact applied suddenly is said to be 3000G or 5000G, and high impact resistance is required for inertial sensors mounted on these devices.
JP 2000-187041 A

  In order to improve the sensitivity of the inertial sensor having the general configuration shown in FIG. 1, the width W of the beam 13 is narrowed, the thickness T is thin, the length L is long, or the weight 12 is heavy. A method is conceivable. However, in general, sensor sensitivity and impact resistance are in an inversely proportional relationship, and when the sensor sensitivity is increased by the above-described method, the impact resistance must be reduced. Conversely, if the shape of the beam 13 or the weight of the weight 12 is designed in order to improve the impact resistance of the sensor, the sensitivity as the sensor is reduced. Thus, there is a problem that it is difficult to achieve both high sensitivity and impact resistance of the inertial sensor.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an inertial sensor including a beam that can achieve both high sensitivity and impact resistance.

  In order to solve this problem, the present invention provides an inertial sensor having a sensing unit configured to suspend a weight as a movable unit with a plurality of beams, and the beam is locally It has an easily deformable part, The easy deformable part is provided avoiding the edge part which is a stress concentration site | part of the said beam, It is characterized by the above-mentioned.

  According to a second aspect of the present invention, in the inertial sensor according to the first aspect, the easily deformable portion is a concave portion having a locally thin thickness, and in the third aspect of the invention, the concave portion is a hole. It is characterized by.

  According to a fourth aspect of the present invention, in the inertial sensor according to the first aspect, the easily deformable portion is a narrow portion provided in a partial region of the beam.

  According to a fifth aspect of the present invention, in the inertial sensor according to any of the first to fourth aspects, a plurality of the easily deformable portions are provided, and the extending direction passing through the center of the beam and the extending direction They are arranged symmetrically with respect to a straight line in a perpendicular direction.

  The invention according to claim 6 is an inertial sensor configured to suspend a weight, which is a movable part, with a beam, and the beam has a shape in which an arbitrary portion of the contour of the beam end has a gentler angle than a right angle. According to a seventh aspect of the present invention, in the inertial sensor of the sixth aspect, the contour of the beam end is a curve.

  The invention according to claim 8 is the inertial sensor according to claim 6 or 7, wherein the beam is provided with the easily deformable portion according to any one of claims 1 to 5. .

  According to a ninth aspect of the present invention, in the inertial sensor according to any one of the first to eighth aspects, a weight stopper that limits a movable range of the weight to a predetermined range is provided in the vicinity of the sensing portion. It is characterized by that.

  According to the present invention, an easily deformable portion (for example, a recess, a hole, or a narrow portion) is provided while avoiding a portion where stress generated in the beam by impact is concentrated, and the easily deformable portion is appropriately disposed. Therefore, it is possible to improve the sensitivity of the sensor without reducing the impact resistance of the sensor.

  In addition, according to the present invention, since the base portion is formed so that the base portion of the beam has a gentler angle without contacting the weight and the frame at right angles, the stress concentration area of the beam base portion is dispersed. The impact resistance can be improved without sacrificing the sensitivity of the sensor.

  Thus, the present invention makes it possible to achieve both high sensitivity and impact resistance of the sensor.

  The best mode for carrying out the present invention will be described below with reference to the drawings. The basic structure of the sensing part of the inertial sensor of the present invention is the same as that shown in FIG. 1, and is built in a silicon substrate by MEMS technology. And this sensing part is mounted on fixing members, such as a glass substrate, and it seals in a package and is made into the element.

  In order to improve the sensitivity of the inertial sensor, in addition to reducing the width of the beam, reducing the thickness, increasing the length, or increasing the weight of the weight, a hole is provided in the beam. A method of facilitating deformation can be considered. However, since the stress distribution generated by the deformation of the beam due to the impact is not uniform, the mechanical strength of the beam is reduced when the hole is provided in the stress concentration portion. Therefore, the beam of the sensing unit provided in the inertial sensor of the present invention is provided with an easily deformable part (such as a concave part whose thickness is set thin) to avoid the part where stress caused by impact is concentrated and the arrangement thereof is devised. Thus, both high sensitivity and impact resistance are achieved.

  First, the stress generated in the beam when an impact is applied will be described. When an impact is applied to the sensing unit, the impact causes a large deformation of the beam, and stress is generated inside.

  FIG. 2 is a diagram for explaining how the beam is deformed when an impact is applied to the inertial sensor. FIG. 2A is a perspective view of the sensing unit in a state where the impact is applied in the x direction. FIG. 2B is a perspective view of the sensing unit in a state where an impact is applied in the z direction. When an impact is applied in the x direction, the weight 12 swings around the beam 13y provided extending in the y direction, and the beam 13x extending in the x direction is greatly bent. . In this case, the base portion R1 and R4 on the frame 14 side and the base portion R2 and R3 on the weight 12 side are bent most greatly, and stress concentrates on these portions. Further, when an impact is applied in the z direction, all four beams 13 are bent, and at this time, the beam 13 is bent most at the base portions R1 and R4 on the frame 14 side and the root portions R2 and R3 on the weight 12 side. Stress is concentrated on these parts.

  As described above, when an impact from the outside is applied, the stress is concentrated at the root portion of the beam 13 and is easily broken by the impact. Therefore, in the inertial sensor of the present invention, an easily deformable portion (such as a concave portion in which the beam thickness is set to be locally thin) is provided at a place avoiding these stress concentration portions. When a concave portion is provided as such an easily deformable portion, the thickness of the concave portion is determined in consideration of various conditions such as the length and width of the beam, the impact resistance to be obtained, or the width of the concave portion. Moreover, it is good also as providing a hole by making the thickness into zero. In the following description, the case where the thickness of the recess is zero will be described as an example.

  3A and 3B are diagrams for explaining the state of the beam hole provided in the sensing unit of the inertial sensor of the present invention. FIG. 3A is a perspective view of the sensing unit, and FIG. 3B is provided in the beam. It is an upper plan view near the beam for explaining the state of the hole. A hole 15 is provided in the beam 13 provided between the weight 12 and the frame 14 so as to avoid the root portion, and the mechanical strength of the beam portion where stress concentration occurs when the beam 13 is deformed is provided. The beam 13 can be easily deformed without dropping, thereby increasing the sensor sensitivity without causing a drop in impact resistance.

  Such a hole is provided so as to avoid the root portion of the width d of the beam 13 having the full length L, and is preferably arranged so as to be symmetric with respect to the midlines AA and BB of the beam 13. . From the viewpoint of improving the sensitivity of the sensor, the width d that avoids the root portion is preferably as small as possible. Therefore, the width d is determined to be minimum in consideration of the relationship with the required impact resistance. In FIG. 3, six such holes 15 are provided, but this is only an example, and the number of holes, their size and shape are considered in relation to the wiring provided on the beam 13 and the like. Designed and optimized.

  According to the confirmation experiment by the inventors, in comparison with an inertial sensor (especially a piezoresistive acceleration sensor that detects a change in stress) having a sensing unit of the same size not provided with a beam hole, It is confirmed experimentally that the sensitivity is improved by about 2 times by providing a hole and that there is no difference in impact resistance with and without the hole, and it is confirmed that high sensitivity can be achieved without reducing the impact resistance. It was done. For example, as shown in FIG. 3C, instead of the beam hole (or together with the beam hole), an extension direction that passes through the center of the beam and avoids an end portion that is a stress concentration portion of the beam, It is good also as providing narrow part 15 'in a line symmetrical position with respect to the straight line of a perpendicular direction. By providing the narrow portion 15 ′, when acceleration is applied in the x-axis direction, the beam is easily twisted in the y-axis direction, and the detection sensitivity is improved.

  In the first embodiment, it has been described that the base shape of the beam is the same as the base shape of the conventional sensing unit. However, from the viewpoint of improving the impact resistance, a device for positively improving the mechanical strength of the beam. Is required. In this embodiment, for the purpose of increasing the mechanical strength of the beam, the impact resistance of the sensor is improved by devising the shape of the root (end) where stress is concentrated when an impact is applied.

  4A and 4B are diagrams for explaining the shape of the beam root portion of the present embodiment. FIG. 4A is a first example of the root portion shape, FIG. 4B is a second example, and FIG. ) Is a diagram showing a conventional root shape. In contrast to the conventional beam illustrated in FIG. 3 of the first embodiment illustrated in FIG. 4C, the conventional beam has a shape in which the root portion in contact with the weight 12 and the frame 14 is a right angle. In this embodiment, the taper (FIG. 4 (a)) and the round (FIG. 4 (b)) are formed so that the base portion of the beam 13 has a gentler angle without contacting the weight 12 and the frame 14 at right angles. A root portion is formed. By adopting such a root portion shape, it is possible to disperse the stress concentration area of the beam root portion and to improve the impact resistance.

  Although it is possible to improve the impact resistance by simply eliminating the right-angled portion as shown in FIG. 4A, it is possible to provide a round as shown in FIG. 4B. A root shape with a gradually changing contour is more effective in improving impact resistance.

  Further, as shown in FIG. 5, for example, in addition to the shape of the root having a taper C (here, 50 μm), it is more effective if the hole provided in the beam 13 has a shape having a radius R (here, 20 μm). It is.

  In addition, since the effect of improving the impact resistance obtained by adopting such a root shape is obtained independently of the effect of improving the sensor sensitivity by providing a hole in the beam, without providing a beam hole. It is apparent that the impact resistance can be improved by forming a root shape having no angle greater than or equal to a right angle in the outline. In addition, the effect of such a root shape can be obtained in the same manner when a narrow portion 15 'is provided instead of (or with a beam hole) as shown in FIG. 4D, for example. Needless to say.

  FIG. 6 is a diagram for explaining an example of the shape of a beam provided in the inertial sensor of the present invention. The beam 13 is provided with a hole 15 arranged in line symmetry with respect to an extending direction passing through the center of the beam 13 and a straight line perpendicular to the extending direction. The piezoresistor 11 provided in the circuit is connected to the electrode 21 provided in the frame 14 by the wiring 22 and outputs a change in resistance value caused by the movement of the weight 12 to a Wheatstone bridge circuit (not shown). Needless to say, these shapes are merely examples and can be changed as appropriate.

  In order to further improve the impact resistance of the inertial sensor having the beam shown in the first to third embodiments, a weight stopper for limiting the movable range of the weight of the sensing unit to a predetermined range is used in this embodiment. Provide.

  FIG. 7 shows a configuration example of weight stoppers provided in the inertial sensor of the present invention. These weight stoppers 16 are finely processed by the MEMS technology and are provided with a certain clearance near the sensing portion. When such a weight stopper 16 is provided, when the weight 12 moves beyond the amount of displacement corresponding to the specified sensitivity range of the sensor, the movement of the weight 12 is hindered by the weight stopper 16, so that a large impact was accidentally applied. Even in such a case, problems such as the beam 13 being greatly deformed or damaged and not functioning as a sensor can be avoided.

  FIG. 8 is a cross-sectional view of the inertial sensor when upper and lower weight stoppers are formed on the package cap and the bottom surface of the package. The sensing unit 17 is fixed to the bottom surface of the package 18 with an adhesive 20, and the package 18 is covered with a cap 19 and stored. A weight stopper as shown in FIG. 7 is formed on the bottom surface of the package 18 and the cap 19.

  The upper and lower surfaces of the weight 12 of the sensing unit may be simple planes, or convex portions may be provided on these surfaces. When such a convex portion is provided, the effective clearance is the distance between the tip surface of the convex portion and the weight stopper surface facing the convex portion. Therefore, there is an advantage that the impact resistance can be improved even when the distance between the weight stopper and the weight is relatively large. In contrast to this, it goes without saying that a similar convex portion may be provided on the weight-facing surface of the weight stopper.

  If the clearance between the weight stopper and the sensing portion (weight) is narrowed, the impact resistance is improved, but the movable range of the weight is narrowed and the dynamic range of the sensor is lowered. On the other hand, if the clearance is wide, the movable range of the weight is widened and the dynamic range of the sensor is widened. However, if the clearance is too large, the weight stopper does not function effectively and the expected impact resistance cannot be obtained. Therefore, the clearance between the sensing unit and the weight stopper provided in the inertial sensor of the present invention is determined so as to satisfy both the dynamic range of the sensor and the impact resistance to be imparted. The clearance is preferably as narrow as possible. This is because if the clearance is made wider than necessary, the weight that started to move due to accidental impact will be greatly accelerated until the movement is restricted by the stopper, and it may be damaged when it hits the stopper. Because it can be considered.

  According to the present invention, it is possible to improve the sensitivity of the sensor without reducing the impact resistance of the sensor, and to improve the impact resistance without sacrificing the sensitivity of the sensor. That is, the present invention makes it possible to achieve both high sensitivity and impact resistance of the sensor.

It is a figure for demonstrating the main structural example of the general inertial sensor which has the basic composition which suspends the weight which is a movable part with a beam, (a) is a perspective view of a sensing part, (b) is an upper surface of a sensing part. FIG. It is a figure for demonstrating a mode that a beam deform | transforms when an impact is applied to an inertial sensor, (a) is a perspective view of the sensing part in the state where the impact was applied to the x direction, (b) is az direction. It is a perspective view of the sensing part in the state where the impact was applied to. It is a figure for demonstrating the mode of the beam hole provided in the sensing part of the inertial sensor of this invention, (a) is a perspective view of a sensing part, (b) is for demonstrating the mode of the hole provided in the beam. (C) is an upper plan view in the vicinity of the beam provided with a narrow portion. It is a figure for demonstrating the shape of the beam base part of Example 2, (a) is a 1st example of a root part shape, (b) is a 2nd example, (c) is a figure which shows the conventional root part shape, And (d) is a figure which shows the base shape of the beam which provided the narrow part. It is a figure for demonstrating the beam which made the hole provided in the beam the shape which gave the radius R in addition to setting it as the root part shape which has the taper C. FIG. It is a figure for demonstrating the example of the shape of the beam with which the inertial sensor of this invention is provided. It is a figure for demonstrating the structural example of the weight stopper with which the inertial sensor of this invention is equipped. It is sectional drawing of an inertial sensor at the time of forming the upper and lower weight stopper in the cap of a package and the bottom face of a package.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Board | substrate 11 Piezoresistor 12 Weight 13 Beam 14 Frame 15 Hole provided in beam 15 'Narrow part 16 Weight stopper 17 Sensing part 18 Package 19 Cap 20 Adhesive 21 Electrode 22 Wiring

Claims (9)

An inertial sensor having a sensing part configured to suspend a weight that is a movable part with a plurality of beams,
The inertial sensor according to claim 1, wherein the beam has an easily deformable portion locally, and the easy deformable portion is provided to avoid an end portion that is a stress concentration portion of the beam. The inertial sensor according to claim 1, wherein the easily deformable portion is a concave portion having a locally thin thickness. The inertial sensor according to claim 2, wherein the recess is a hole. The inertial sensor according to claim 1, wherein the easily deformable portion is a narrow portion provided in a partial region of the beam. 5. The plurality of easily deformable portions are provided, and are arranged symmetrically with respect to an extending direction passing through the center of the beam and a straight line perpendicular to the extending direction. The inertial sensor according to any one of the above. An inertial sensor configured to suspend a weight, which is a movable part, with a beam,
The inertial sensor according to claim 1, wherein the beam has a shape in which an arbitrary portion of the contour of the beam end has a gentler angle than a right angle. The inertial sensor according to claim 6, wherein a contour of the beam end portion is a curve. The inertial sensor according to claim 6 or 7, wherein the beam is provided with the easily deformable portion according to any one of claims 1 to 5. The inertial sensor according to any one of claims 1 to 8, wherein a weight stopper that limits a movable range of the weight to a predetermined range is provided in the vicinity of the sensing unit.

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